
There is plenty on this site re Breguet numbering system and it seems that the simple answer according to the posts here are that;
Breguet follow a procedure to number their watches in a sequence from 250 to 5500 followed by a letter.
The numbers are applied to the overall production rather than a model type so that your 5140 might be 737Z and the next watch might be Serial number 738Z but it is a Model 5177 or Model 3130 or whatever.
The reason given that this is done this way is because A Breguet numbered his first watch as 250 and watches in earlier times went up to Serial No. 5,500 at which time the sequence started over again with a letter following the number.
It seems that some owners of the Breguet company ignored thois system for a short while and there are some watches numbered up into the 9,000, but then Breguet reverted back to the current system.
This system allows a max of 4 digits, which suit the brand habit of displaying the serial number on the silver engraved face, and when you turn the watch over you will find the same number on the back with a letter.
Hope that helps. Enjoy your Breguet 5140.
I made my decision this morningon which Breguet to buy, and just returned from sending the money, but as my AD is 3,000 kms away I have to wait a couple of days....it will be a long two days.
Reagrds,
Jack